What is a mast cell tumor (MCT)?

Mast cells are part of the body’s immune system, and can be found in the skin, lungs, and intestinal tract. An MCT is an abnormal growth of mast cells, found most commonly in dogs in the skin. A mast cell tumor contains histamine granules that when released, can cause gastrointestinal signs, or allergic reactions. Mast cell tumors are staged as “low-grade” or “intermediate- to high-grade,” according to the degree of malignancy and risk of spread (i.e., metastasis) to other organs. Certain breeds are predisposed to developing mast cell tumors. An MCT can mimic benign growths on or under the skin.

What are common MCT signs in dogs?

Early signs include:

• A skin tumor, possibly pink or red in color

• Rapid tumor growth or disappearance

Intermediate to advanced signs include: 

• Multiple tumors

• Tumor rupture

• Enlarged lymph nodes

• Lethargy

• Loss of appetite

• Vomiting or diarrhea

• Distended abdomen

• Collapse

How are MCTs managed in dogs?  

Complete surgical excision of a mast cell tumor is the preferred treatment. Depending on the tumor grade or metastasis signs, MCT management can include radiation therapy and/or chemotherapy. Corticosteroids can lead to a brief remission. Palliative medications may be recommended, to prevent systemic or gastrointestinal effects. Discussing a personalized management plan with your veterinarian, and a veterinary oncologist, is important for the best outcome for your dog. 

What is the prognosis for dogs with an MCT?

The prognosis depends on successful surgical tumor removal, and the MCT malignancy grade. Complete excision of a low-grade MCT is often curative. Dogs with higher-grade tumors, internal tumors, metastasis, or tumors that recur quickly have a poorer prognosis.  

Management tips for dogs with an MCT 

At-home needs include:

• Easy access to food and water, and a comfortable location

• Consistency with prescribed medications

• Close monitoring for tumor recurrence, or systemic disease signs

• Post-surgical care as recommended by your veterinarian

In a crisis situation:

Contact your veterinarian immediately if your dog develops excessive swelling or drainage at the surgery site, new tumors, lethargy, loss of appetite, vomiting, or diarrhea; collapses; or vocalizes in pain.